Duration of Mineralization in Young Porphyry Systems through Rhenium-Osmium (Re-Os) Dating

Colorado State University, Fort Collins CO

Investigators

Abstract

Stein EAR-0087483 This project addresses one of the fundamental underpinnings needed to understand geologic processes that produce copper-molybdenum deposits associated with magmatism at shallow levels in the earth's crust. This underpinning is the timing and duration of the mineralization process within the broader context of the magmatism and the tectonic and geologic evolution of a terrane. It has been said: "No Dates, No Rates!" Using the now established Re-Os (rhenium-osmium) method of dating, the only method that directly dates the sulfide ore minerals themselves, this study addresses the time span needed to form so-called porphyry copper-molybdenum deposits. Do they form over tens of millions of years (or more), or do they form in a few hundred thousand years (or less)? Previous attempts at dating the time of ore deposition were limited by techniques that addressed presumably ore-associated minerals and/or techniques that do not retain the age of mineralization. For example, one dating technique involves the use of Ar (argon), a gas in its natural state, and although Ar may be found and measured in rocks and minerals, this is not a comfortable site for the element. In contrast, both Re and Os are sulfide-loving, and are naturally concentrated in metallic ore minerals. The results from this Re-Os study will be compared with age results derived from other methods of dating. This study will focus on dating mineralization associated with two young magmatic systems that host giant deposits of molybdenum and copper, the classic Henderson molybdenum deposit in Colorado and the Los Pelambres copper-molybdenum deposit in Chile.